1. Field of the Invention
The present invention concerns an electronic control device for a bistable solenoid valve with automatic low battery protection, particularly for watering systems.
2. Description of Related Art
Watering systems for lawns, gardens, kitchen gardens and cultivated spaces are generally based on the use of solenoid valves that determine the delivery of water in the various sectors to be watered.
The control of the solenoid valves is entrusted to programmable electronic control devices having various degrees of complexity that can be connected with mains power or operate with battery power, in which case, for power saving reasons, valves with bistable type electric actuators are essential.
With battery operated devices, the battery runs down and it is then necessary to detect the low or exhausted battery condition and to operate the solenoid valves in order to lock them in a closing position. In this way, considering that bistable type solenoid valves require driving controls of short duration, it is possible to prevent the opening of the solenoid valve whilst the battery still has sufficient energy to control the opening of the solenoid valve, but insufficient energy to subsequently close the solenoid valve, with the consequence that watering would continue without interruption until the moment in which someone notices the problem.
For such reason battery-operated control devices are usually provided with electronic circuits capable of detecting the battery voltage dropping to a minimum value, below which no further activation of the solenoid valves being controlled will occur.
In this way, the detection circuit determines the locking of the system when in reality the battery still has sufficient energy for several additional activations.
In addition, the detection circuit has a cost of its own, that obviously affects the total cost of the control device.
An object of the present invention is to realize a battery operated electronic control device for a bistable type solenoid valve, particularly but not exclusively for watering systems, that does not require a detection circuit for detecting a low or exhausted battery condition.
According to a first aspect of the invention such object has been attained with an electronic control device for bistable solenoid valve, comprising: a power supply battery; a capacitor in parallel with the battery; a switch having first switching means interposed between the battery and the capacitor and second switching means interposed between the capacitor and the bistable solenoid valve, said switch having a first operating position (rest position), in which the capacitor is connected to the battery to receive charge therefrom and is disconnected from the solenoid valve and second and third operating positions in which the capacitor is disconnected from said battery and is connected to the solenoid valve to transfer control voltages having opposite signs from the capacitor to the solenoid valve for respectively causing closing and opening of the solenoid valve; and a programmed logic control unit which controls said switch so that at each request for the opening of the solenoid valve the switch operates, in succession, first switching from said first operating position to said second operating position for the closing of the solenoid valve after a first preset time has elapsed from a previous valve closing operation, then switching to said first operating position and finally switching to said third operating position for the opening of the solenoid valve after a second preset time from said second switching, said second preset time being shorter than said first preset time.
According to a second aspect of the invention, there is provided an electronic control device for a bistable solenoid valve, comprising: a power supply battery; a capacitor in parallel with the battery; and a programmed logic control unit which at each request for opening of the solenoid valve controls, in succession, a first charge of the capacitor from the battery for a first preset time, a first discharge of the capacitor for a closing operation of the solenoid valve, a second charge of the capacitor from the battery for a second preset time which is shorter than said first preset time, and a second discharge of the capacitor for an opening operation of the solenoid valve.
Thus, as will be better seen hereinafter, it is possible to have a guarantee that at a certain point of discharging of the battery, or even in case of removal of the battery, a residual energy remains in the capacitor that is capable of allowing the closing of the solenoid valve without any further possibility of opening it again.